Epos refers to a word or spoken utterance — from the same root that gives us 'epic' poetry. In the New Testament it appears only in Hebrews 7:9, in the phrase hōs epos eipein — 'so to speak' or 'one might even say.' This use is idiomatic, meaning 'in a manner of speaking.' The word is related to the Greek verb epō (to speak/say) and ultimately to logos in the sense of divine utterance. In classical Greek, epos was specifically the word for bardic/poetic speech.
Though epos itself appears only once in the NT in a parenthetical phrase, its significance lies in its association with the divine word (logos) and the Hebrew concept of dabar. The author of Hebrews uses it to make a daring theological claim: Levi paid tithes to Melchizedek — 'so to speak' — while still in the loins of Abraham. This is a bold move in typological theology: the lesser (Levi/the Aaronic priesthood) is shown to have already acknowledged the greater (Melchizedek/Christ's priesthood) in a figurative, typological sense.